This invention relates to the drying of decorated cylindrical objects such as two-piece metal cans, and more specifically relates to a novel drying system in which the can decoration material consists of thermally dryable inks, varnishes and coatings and in which a gas flame is impinged directly on the decorated can surface.
In the manufacture of a two-piece metal can for containing beverages and the like, the can body is formed and, before it is filled and the top put in place, the can is decorated, as by first placing a base coat on the can and printing a label on the can, and then placing an overvarnish layer on the can. Apparatus for performing these decorating operations are well known, and one high speed device which can decorate cans at rates in excess of 800 can per minute is shown in U.S. Pat. No. 3,766,851 to Sirvet et al, assigned to the assignee of the present invention. This apparatus has a transfer mechanism for transferring the decorated cans to a pin-chain conveyor which conveys the cans to a suitable drying oven.
It is conventional to term apparatus for printing on cans, and for applying overvarnish on cans, as "can decorators" and it is conventional to term apparatus for coating cans as "can coaters". For convenience, the term "can decorator" used herein shall be intended to apply equally to apparatus for individually or collectively printing, coating or varnishing cans. The term "decorating medium" used herein is to refer to any ink, varnish or coating which is applied by the can decorator apparatus.
Presently used drying ovens for curing conventional inks and coatings consist of large, hot air, convection type ovens. When the inks and coatings used for the decoration are ultraviolet curable materials, the curing oven will contain ultraviolet lamps disposed along the path of movement of the decorated cans. A typical ultraviolet curing oven for curing decorated cans is shown in U.S. Pat. No. 3,840,999 in the name of Edward J. Whelan, and assigned to the assignee of the present invention.
The conventional hot air oven takes about 60 to 90 seconds or more to cure a decorated can. Consequently, the oven requires a large volume so that the rapidly moving can remains in the oven for the necessary curing time. Thus, even when the can path is festooned within the oven, the oven requires a large floor space and volume. The flame drying system has been found to cure a decorated can in about three seconds or less. Consequently, the drying stage requires only a small fraction of the area and volume required for the hot air oven.
The use of flame drying will be far more efficient than the hot air oven, and gas consumption will be reduced as compared with the conventional hot air oven. Moreover, the direct flame impingement process will cause the volatile substances driven off during the drying process to be at least partially combusted, thus reducing or completely eliminating the need for afterburning devices to meet current pollution standards.
The system of the present invention is advantageous over present ultraviolet curing systems since the invention allows the use of conventional heat set or thermally cured inks and coatings, as opposed to special ultraviolet curable inks and coatings which are more expensive and not as readily available as conventional heat set inks.